This invention relates to elongated flexible probes, such as borescopes and endoscopes, and is more particularly directed to a torsional strain relief that absorbs torsional stress at the proximal end of a borescope or endoscope insertion tube.
A borescope is generally characterized as an elongated flexible insertion tube with a viewing head at its distal or forward end, and a control section at its proximal end for controlling the bending at the distal end. In such a borescope, a bendable tube steering section is situated at the distal end adjacent to the viewing head. Typically, control cables extend through the bendable tube section and the remainder of the insertion tube and connect with a steering control mechanism in the control section. These cables are differentially displaced for bending the steering section to facilitate the inspection of a remote object.
A borescope is typically intended for visual inspection of an intricate mechanical assembly, such as a jet engine or turbine, or a heat exchanger tube, where it would be difficult or impossible otherwise to view the assembly's internal elements. The borescope needs to be insertable into narrow, tortuous passageways, and must observe very delicate steering considerations. It often occurs, because of the many bends that the insertion tube must undergo, that a torsion or twisting force is applied onto the insertion tube, which can produce a rotational strain at the junction of the insertion tube with the control section.
An endoscope is typically inserted into a body cavity of a human or veterinary patient for visual inspection of tissues within the cavity. Because body passages such as esophagus, bronchi, and colon are narrow and tortuous, the steering section must be bent rather precisely, and as close to the viewing head as possible. Thus, cable tension must be limited and cable slack minimized as much as possible. In many types cf diagnosis or treatment, such as in the colon or the small intestine, the probe insertion tube is subjected to a large number of bends. These can impose a twisting force on the insertion tube.
In either type of probe, the twisting of the insertion tube can produce a loss of alignment of the viewing head, and the degree and direction of misalignment is difficult or impossible to estimate.
Currently, insertion tubes are of a torsionally stiff design, and although they will bend, they are not free to rotate about their own axis. Accordingly, if this type of insertion tube is forced to twist, the force will be absorbed at the weakest point, i.e. the junction of the proximal end of the insertion tube with the control section housing or frame. This can cause delamination of the insertion tube, particularly in an outer braid layer.
Borescopes and/or endoscopes of this general type are described in various U.S. Patents, e.g., U.S. Pat. Nos. 4,253,447; 4,261,344; 4,491,865. A similar type of probe is shown in U.S. Pat. No. 4,621,618 to Omagari. Further examples are described in U.S. Pat. Nos. 4,546,379; 4 523,224; 4,532,918, and 4,539,586. Various steering mechanisms for articulated, elongated flexible probes are described, e.g. in U.S. Pat. Nos. 3,610,231; 3,739,770; 3,593,393; 3,669,098; 3,779,151; 4,347,837 and 4,700,693. An alternative arrangement is described in U.S. Pat. No. 4,794,912. A review of this patent literature will provide a general background and understanding of borescopes, endoscopes, and similar probes.